Time 0 Void Evolution and Effect on Electromigration

In this study, an Electromigration (EM) acceleration test was conducted at 150 oC ambient temperature with 12A current. The solder joint was made of SAC305. Time 0 void evolution was observed by X-ray. A Finite Element Analysis (FEA) based on Atom Flux Divergence (AFD) and vacancy concentration were introduced. The detail of simulation process is given. The results show that location and size play an essential role in EM failure. On the cathode side of a solder ball, the void position would slightly increase the TTF, temperature and current density, However, a larger void size will significantly increase the TTF, temperature and current density. On the anode side, time 0 void barely affects the TTF, temperature and current density. Avoiding the time 0 void on the substrate side will significantly improve the EM performance because the Cu pad is thicker than Cu trace in general.